Double tunnel junction with magnetoresistance enhancement layer

ABSTRACT

An apparatus and method is disclosed for an enhanced double tunnel junction sensor which utilizes an enhancement layer(s) to enhance magnetoresistance (MR coefficient) and resonant tunneling. Additionally, a combined read/write head and disk drive system is disclosed utilizing the enhanced double tunnel junction sensor of the present invention. The enhancement layers improve the resonant tunneling and boost the MR coefficient to achieve a higher tunnel magnetoresistance (TMR) for the structure with applied dc bias. This is accomplished by using enhancement layers that create a quantum well between the enhancement layer and the pinned layer, which causes resonance, enhancing the tunneling electrons. By doing this, the tunneling constraints on the free layer are decoupled, allowing the free layer to be made thicker which results in reducing or eliminating free layer magnetic saturation caused by an external magnetic source. As the enhanced double tunnel junction sensor is positioned over the magnetic disk, the external magnetic fields sensed from the rotating disk moves the direction of magnetic moment of the free layer up or down, changing the resistance through the tunnel junction sensor. As the tunnel current is conducted through the tunnel junction sensor, the increase and decrease of electron tunneling (i.e., increase and decrease in resistance) are manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry of the disk drive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a double tunnel junction structure usedas a tunnel junction sensor in a magnetic head, and more particularly,to a double tunnel junction structure having enhancement layers thatboost the magnetoresistance with multiple barriers used to eliminate theeffect of the applied dc bias without reduction in spin polarizedtunneling.

2. Description of the Related Art

A read head employing a read sensor may be combined with an inductivewrite head to form a combined magnetic head. In a magnetic disk drive,an air bearing surface (ABS) of the combined magnetic head is supportedadjacent a rotating disk to write information on or read informationfrom the disk. Information is written to the rotating disk by magneticfields which fringe across a gap between the first and second polepieces of the write head. In a read mode, the resistance of the readsensor changes proportionally to the magnitudes of the magnetic fieldsfrom the rotating disk. When a current is conducted through the readsensor, resistance changes cause potential changes that are detected andprocessed as playback signals.

A read sensor is employed by a magnetic head for sensing magnetic fieldsfrom moving magnetic media, such as a magnetic disk or a magnetic tape.One type of read sensor employs a tunnel junction sensor. The typicaltunnel junction sensor includes a nonmagnetic spacer layer sandwichedbetween first and second ferromagnetic layers, commonly called a pinnedlayer, and a free layer. The magnetization of the pinned layer is pinned90° to the magnetization of the free layer and the magnetization of thefree layer is free to respond to external magnetic fields. Themagnetization of the pinned layer is typically pinned by exchangecoupling with an antiferromagnetic pinning layer.

The tunnel junction sensor is based on the phenomenon of spin-polarizedelectron tunneling. The typical tunnel junction sensor usesferromagnetic metal electrodes, such as NiFe or CoFe, having highcoercivity with a spacer layer that is thin enough that quantummechanical tunneling occurs between the ferromagnetic layers (FM/IFM).The tunneling phenomenon is electron spin dependent, making the magneticresponse of the tunnel junction sensor a function of the relativeorientations and spin polarization of the two ferromagnetic layers. Thedetails of tunnel junction structures have been described in thecommonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which isincorporated by reference herein.

FIG. 1 shows tunnel magnetoresistance (TMR) as a function of dc bias fora tunnel junction sensor. At low dc bias, the conduction varies onlyslightly with the dc bias. As the dc bias increases, the TMR coefficientdrops noticeably. For example, the application of 300 mV bias across atunnel junction structure having a structure comprisingferromagnetic/insulator/ferromagnetic (FM/I/FM) reduces the TMR by half.

To solve this problem, another type of tunnel junction sensor has beenproposed called a double junction sensor (FM/I/FM/I/FM). FIG. 2 shows aprior art tunnel junction sensor 200 which includes a first pinninglayer 205, a first pinned layer 210, a first spacer layer 215, a freelayer 220, a second spacer layer 225, a second pinned layer 230 and asecond pinning layer 235. The magnetization of the outer two FM pinnedlayers are parallel while the magnetization of the internal FM freelayer is either parallel or antiparallel. Modeling has shown that thedouble tunnel junction behaves differently than the traditional singletunnel junction by eliminating the effect of dc bias. FIG. 3 shows theTMR as a function of the dc bias for a double junction tunnel junctionsensor.

While it appears that the multiple barriers have been shown tosignificantly eliminate the effect of dc bias, the double tunneljunction has drawbacks. For the spin polarized resonant tunnelingphenomenon to work, the layers of the double tunnel junction must bemade very thin. While it is desired to have thin layers, too thin alayer is detrimental to the device. For example, the center FM layer(traditionally the free layer) for the prior art is between 10 and 20 Å.With a layer this thin, the ferromagnetic free layer becomes saturatedeasily from external magnetic fields. Once saturated, the double tunneljunction sensor does not get the full benefit of the ferromagnetic freelayer, the signals get clipped. It is preferable that the free layernever be saturated.

From the above discussion it becomes apparent that what is needed is adouble tunnel junction sensor that provides the benefits of improvedspin polarized tunneling and minimizing dc bias effects while alsoproviding a device in which the internal layers are not saturated by anexternal magnetic field.

SUMMARY OF THE INVENTION

The present invention is directed toward an enhanced double tunneljunction structure that has enhancemnt layers causing resonant tunnelingwhich boosts the magnetoresistance (MR), achieving higher tunnelmagnetoresistance (TMR) for the structure. This is accomplished by usingenhancement layers that create a quantum well between the enhancementlayer and the pinned layer. By doing this, the tunneling constraints onthe free layer are decoupled, allowing the free layer to be made thicker(>20 Å) and reducing or eliminating saturation from an external magneticsource.

In one embodiment, the resonant enhanced double tunnel junction sensorincludes a first shield, a first pinning layer, a first pinned layer, afirst enhancement layer, a first spacer layer, a free layer, a secondspacer layer, a second enhancement layer, a second pinned layer, asecond pinning layer and a second shield layer. In the preferredembodiment, the enhancement layer is made form copper (Cu). In anotherembodiment, the free layer is a multi-layered material having 75% NiFeand 25%Co₉₀Fe₁₀.

In the preferred embodiment, the magnetic moment of the first and secondpinned layers are pinned by interfacial exchange with the magnetic spinsof the first and second pinning layers in a downward direction,perpendicular to the ABS, while the magnetic moment of the free layer isperpendicular to the magnetic moment of the first and second pinnedlayers (i.e., the moment direction being parallel to the ABS). In use, atunneling current I_(T), using spin dependent electron tunneling, flowsthrough the enhanced double tunnel junction sensor, using the first andsecond shield layers as leads. The amount of current I_(T) that flowsthrough is dependent on the relative magnetic moment directions betweenthe first and second pinned layers and the free layer. In prior artdouble tunnel junctions, the free layer must be thin to perform properlyand is prone to become saturated quickly from the external magneticfield. To solve this problem, the present invention adds enhancementlayers of copper (Cu) to boost the magnetoresistivity (MR) of thesensor. The copper enhancement layers increase the spin polarizedresonant tunneling, giving the structure a high TMR. With the higherTMR, the free layer may be made thicker and not saturate as easily. Asthe enhanced double tunnel junction sensor is positioned over themagnetic disk, the external magnetic fields sensed from the rotatingdisk moves the direction of magnetic moment of the free layer up ordown, changing the resistance through the tunnel junction sensor. As thetunnel current I_(T) is conducted through the sensor, the increase anddecrease of electron tunneling (i.e., increase and decrease inresistance) are manifested as potential changes. These potential changesare then processed as readback signals by the processing circuitry.

Another embodiment of the present invention is an antiparallel (AP)resonant enhanced double tunnel junction sensor. This AP double tunneljunction sensor is similar to the double tunnel junction sensordescribed above but utilizes first and second AP pinned layers and inplace of the first and second pinned layers. The AP pinned layerconsists of a spacer made of ruthenium (Ru) between pinned film layers,preferably made of cobalt (Co). Because of the antiparallel features ofthe AP layers due to the Ru spacer layer, the magnetic moment of the onepinned film is antiparallel to magnetic moment of the other pinned film,which increases the effect of the sensor when the magnetic moment of thefree layer rotates. In other embodiments, a combinations of pinned andAP pinned layers are used.

Other objects and advantages of the present invention will becomeapparent upon reading the following description taken together with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of tunnel magnetoresistance (TMR) vs. dc bias for atraditional tunnel junction structure (FM/I/FM);

FIG. 2 is an air bearing surface (ABS) illustration of a prior artdouble tunnel junction structure (FM/I/FM/I/FM);

FIG. 3 is a graph of TMR vs. dc bias for the structure of FIG. 2;

FIG. 4 is a plan view of an exemplary magnetic disk drive;

FIG. 5 is an end view of a slider with a magnetic head as seen in plane5—5 of FIG. 4;

FIG. 6 is an elevation view of the magnetic disk drive wherein multipledisks and magnetic heads are employed in a housing;

FIG. 7 is an isometric illustration of an exemplary suspension systemfor supporting the slider and magnetic head;

FIG. 8 is an ABS view of the slider taken along in plane 8—8 of FIG. 5;

FIG. 9 a side view of a front portion of the magnetic head as seen inplane 9—9 of FIG. 5;

FIG. 10 is a partial ABS view of the slider taken along plane 10—10 ofFIG. 9 to show the read and write elements of the magnetic head;

FIG. 11 is a view taken along plane 11—11 of FIG. 9 with all materialabove the coil layer and its leads removed;

FIG. 12 is an air bearing surface (ABS) illustration of one embodimentof the sensor of the present invention;

FIG. 13 is an air bearing surface (ABS) illustration of anotherembodiment of the sensor of the present invention; and

FIG. 14 is an illustration of alternate embodiments using multi-layerconstruction for the free layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Magnetic Disk Drive

Referring now to the drawings wherein like reference numerals designatelike or similar parts throughout the several views, FIGS. 4-6 illustratea magnetic disk drive 30. The drive 30 includes a spindle 32 thatsupports and rotates a magnetic disk 34. The spindle 32 is rotated by amotor 36 that is controlled by a motor controller 38. A combined readand write magnetic head (merged MR head) 40 is mounted on a slider 42that is supported by a suspension 44 and actuator arm 46. A plurality ofdisks, sliders and suspensions may be employed in a large capacitydirect access storage device (DASD) as shown in FIG. 3. The suspension44 and actuator arm 46 position the slider 42 so that the magnetic head40 is in a transducing relationship with a surface of the magnetic disk34. When the disk 34 is rotated by the motor 36 the slider is supportedon a thin (typically, 0.05 μm) cushion of air (air bearing) between thesurface of the disk 34 and the air bearing surface (ABS) 48. Themagnetic head 40 may then be employed for writing information tomultiple circular tracks on the surface of the disk 34, as well as forreading information therefrom. Processing circuitry 50 exchangessignals, representing such information, with the head 40, provides motordrive signals for rotating the magnetic disk 34, and provides controlsignals for moving the slider to various circular tracks on the disk.FIG. 7 shows the mounting of the slider 42 to the suspension 44, whichwill be described hereinafter. The components described hereinabove maybe mounted on a frame 54 of a housing 55, as shown in FIG. 6.

FIG. 8 is an ABS view of the slider 42 and the magnetic head 40. Theslider has a center rail 56 that supports the magnetic head 40, and siderails 58 and 60. The rails 56, 58 and 60 extend from a cross rail 62.With respect to rotation of the magnetic disk 34, the cross rail 62 isat a leading edge 64 of the slider and the magnetic head 40 is at atrailing edge 66 of the slider.

FIG. 9 is a cross-sectional elevation side view of a front portion ofthe merged MR head 40, which includes a write head portion 70 and a readhead portion 72, the read head portion employing an enhanced doubletunnel junction sensor 74 of the present invention. FIG. 10 is an ABSview of FIG. 9. The sensor 74 and insulating gap layer 75 are sandwichedbetween first and second shield layers 80 and 82. The insulating gaplayer 75 insulates the shields from each other and may be made fromaluminum oxide, aluminum nitride or silicone dioxide. In response toexternal magnetic fields from the rotating disk, the resistance of thetunnel junction sensor 74 changes. To determine the resistance, atunneling current I_(T) is used. The first and shield layers 80 and 82are employed as leads. The current flows through all the layers of thetunnel junction between the leads (i.e., first and second shields). Asthe free layer rotates in response to the magnetic field from the disk,the resistance of the tunnel junction structure changes, altering thecurrent through the structure. These resistance changes are manifestedas potential changes. These potential changes are then processed asreadback signals by the processing circuitry 50 shown in FIG. 6.

The write head portion of the merged MR head includes a coil layer 84sandwiched between first and second insulation layers 86 and 88. A thirdinsulation layer 90 may be employed for planarizing the head toeliminate ripples in the second insulation layer caused by the coillayer 84. The first, second and third insulation layers are referred toin the art as an “insulation stack”. The coil layer 84 and the first,second and third insulation layers 86, 88 and 90 are sandwiched betweenfirst and second pole piece layers 92 and 94. The first and second polepiece layers 92 and 94 are magnetically coupled at a back gap 96 andhave first and second pole tips 98 and 100 which are separated by awrite gap layer 102 at the ABS. As shown in FIGS. 5 and 7, first andsecond solder connections 104 and 116 connect leads from the tunneljunction sensor 74 to leads 112 and 124 on the suspension 44, and thirdand fourth solder connections 118 and 116 connect leads 120 and 122 fromthe coil 84 to leads 126 and 114 on the suspension.

Present Invention

The present invention is directed toward an enhanced double tunneljunction structure that has enhancement layers. These enhancement layersboost the MR to achieve a higher TMR for the structure. This isaccomplished by using enhancement layers to create a quantum wellbetween the enhancement layer and the pinned layer causing resonancewhich enhances the tunneling electrons. By doing this, the tunnelingconstraints on the free layer are decoupled, allowing the free layer tobe made thicker (>20 Å) and reducing or eliminating saturation of thefree layer from an external magnetic source. FIG. 12 shows oneembodiment of the present invention of a resonant enhanced double tunneljunction sensor 300 which includes a first shield 80, a first protectionlayer 302 (if necessary), a seed layer 303 (if necessary), a firstpinning layer 305, an interface layer 306, a first pinned layer 310, afirst enhancement layer 314, a first spacer layer 315, a free layer 320,a second spacer layer 325, a second enhancement layer 326, a secondpinned layer 330, an interface layer 332, a second pinning layer 335, asecond protection layer 337 (if necessary) and a second shield layer 82.The first and second shields, 80 and 82, are made from a conductivematerial, such as Permalloy, which is Ni₈₀Fe₂₀. The first and secondprotection layers 302 and 337 are made of tantalum (Ta), having athickness of 10-100 Å, with a preferred thickness of 50 Å. Theprotection layers are used to protect the sensor from damage duringsubsequent processing and to isolate the sensor from the shields. Theprotection layers are also known as de-coupling layers. Depending on theprocessing, the protection layers may not be necessary. The seed layer303 is made of nickel iron (NiFe) with a thickness of 10-20 Å. The seedlayer is used to control the grain size, texture and crystal structure.In certain instances, the seed layer may not be necessary. The first andsecond pinning layers, 305 and 335, are preferably made of anantiferromagnetic material, such as platinum manganese (PtMn), with athickness range of 50-250 Å, preferably 100 Å. In the preferredembodiment, the magnetic spins of the first and second pinning layersare parallel with each other. Optionally, the pinning layers may be madeof manganese iron (MnFe), nickel manganese (NiMn) or iridium manganese(IrMn). The interface layers 306 and 332 are made of nickel iron (NiFe),with a thickness of 10-30 Å, preferably 20 Å, and are used between thepinning layers and the pinned layers to enhance exchange coupling. Thereason for the interface layers is that the pinning layer material has astronger exchange coupling with the NiFe material than the pinned layermaterial. The first and second pinned layers, 310 and 330, arepreferably made from a ferromagnetic material, such as cobalt iron (Co₉₀Fe₁₀), with a thickness of 20-60 Å, preferably 40 Å. Optionally, thepinned layers may be made from nickel iron (NiFe) or Cobalt (Co). Thefirst pinned layer 310 is exchange coupled to the first pinning layer305 and the second pinned layer 330 is exchange coupled to the secondpinning layer 335. In the preferred embodiment, the magnetic moment ofthe first and second pinned layers, 310 and 330, are parallel. The firstand second enhancement layers, 314 and 326, are preferably made ofcopper (Cu), with a thickness of 10 Å. Optionally the enhancement layersmay be made from aluminum (Al) or any other conductive material thatincreases spin polarized resonant tunneling. The first and second spacerlayers, 315 and 325, are preferably made of aluminum oxide, with athickness of 10-30 Å, preferably 20 Å. The free layer 210 is made fromnickel iron (NiFe), with a thickness of 30-100 Å, preferably 40 Å.Optional embodiments of the free layer use a multi-layer construction ofmaterial and thicknesses having 75% NiFe and 25%Co₉₀Fe₁₀. FIG. 14 showsexamples of the multi-layer free layers. Multi-layer free layer 360 iscomprised of a 5 Å cobalt iron (Co₉₀Fe₁₀) first layer 361, a 30 Å nickeliron (NiFe) second layer 362 and a 5 Å cobalt iron (Co₉₀Fe₁₀) thirdlayer 363. Multi-layer free layer 365 is comprised of a 10 Å cobalt iron(Co₉₀Fe₁₀) first layer 366 and a 30 Å nickel iron (NiFe) second layer367. While the above description presents material options for thevarious layers, it is understood that equivalent materials may besubstituted and fall within the scope of the present invention.

In the preferred embodiment, the magnetic moment of the first and secondpinned layers, 310 and 330, are pinned in a downward directionperpendicular to the ABS, due to interfacial exchange with the magneticspins of the adjacent first and second pinning layers, 305 and 335. Themagnetic moment of the free layer 320 is in a different direction thanthe pinned layers, such as a canted relationship, preferablyperpendicular to the magnetic moment of the first and second pinnedlayers, 310 and 330 (i.e., the moment direction being parallel to theABS). In use, a tunneling current I_(T), using spin dependent electrontunneling, flows through the tunnel junction sensor 300, using the firstand second shield layers, 80 and 82, used as leads. The amount ofcurrent I_(T) that flows through is dependent on the relative magneticmoment directions between the first and second pinned layers 310 and 330and the free layer 320. As the tunnel junction sensor 300 is positionedover the magnetic disk 34, the external magnetic fields sensed from therotating disk 34 moves the direction of magnetic moment of the freelayer 320 up or down, changing the resistance through the enhanceddouble tunnel junction sensor 300. The use of the resonant enhancementlayers, 314 and 326, further enhance the change in resistance (ΔR/R) ofthe enhanced double tunnel junction sensor 300. As the magnetic momentof the free layer 320 rotates up from the ABS (i.e., going toward theopposite direction of the magnetic moment of the first and second pinnedlayers, 310 and 330), the amount of electron tunneling decreases (i.e.,the resistance increases). As the magnetic moment of the free layer 320rotates down toward the ABS (i.e., going toward the same direction asthe magnetic moment of the first and second pinned layers, 310 and 330),the amount of electron tunneling increases (i.e., the resistancedecreases). As the tunnel current I_(T) is conducted through the sensor300, the increase and decrease of electron tunneling (i.e., increase anddecrease in resistance) are manifested as potential changes. Thesepotential changes are then processed as readback signals by theprocessing circuitry shown in FIG. 6. To boost the magnetoresistivity(MR) of the sensor 300, the copper (Cu) enhancement layers arepositioned next to the spacer layers of aluminum oxide. The copperenhancement layers increase the spin polarized resonant tunneling,giving the structure a high TMR. With the higher TMR, the free layer maybe made thicker and not saturate as easily.

FIG. 13 is another embodiment of the present invention showing anantiparallel (AP) resonant enhanced double tunnel junction sensor 350.This sensor double tunnel junction sensor 350 is similar to the doubletunnel junction sensor 300 described above but utilizes a first andsecond AP pinned layers, 340 and 345, in place of the first and secondpinned layers, 310 and 330. The first AP pinned layer 340 consists of aspacer 342, made of ruthenium (Ru), with a thickness of 8 Å, locatedbetween a first pinned film 341 and a second pinned film 343, preferablymade of cobalt (Co), with a thickness of 25 Å and 20 Å respectively. Thesecond AP pinned layer 345 consists of a spacer 347, made of ruthenium(Ru), with a thickness of 8 Å, located between a third pinned film 346and a forth pinned film 348, preferably made of cobalt (Co), with athickness of 20 Å and 25 Å respectively. Optionally, the pinned filmsmay be made of nickel iron (NiFe). Because of the antiparallel featuresof the AP pinned layer 340 due to the Ru spacer layer, the magneticmoment of the first pinned film 341 is in the same direction as themagnetic spins of the first pinning layer 305 by interfacial exchange,while the magnetic moment of the second pinned film 343 is in anantiparallel direction. Similarly, the direction of the magnetic momentof the forth pinned layer 348 is pinned by interfacial exchange with theadjacent second pinning layer 335, with the preferred embodiment in adownward direction perpendicular to the ABS. Because of the antiparallelfeatures of the AP pinned layer 345 due to the spacer layer 347, themagnetic moment of the third pinned film 346 is antiparallel to magneticmoment of the forth pinned film 348. Having the magnetic moments of thesecond and third pinned film layers, 343 and 346, antiparallel to themagnetic moments of the first and forth pinned film layers, 341 and 348,increases effect of the sensor when the magnetic moment of the freelayer 320 rotates. In another embodiment, a combination of a pinnedlayer (310 or 330) and an AP pinned layer (340 or 345) is used. In thisembodiment, the pinned layer 310 is used with AP pinned layer 345 or thepinned layer 330 is used with AP pinned layer 340. In still anotherembodiment, the multi-layer free layer 360 or 365 (see FIG. 14) is usedwith AP pinned layers 340 and 345 or used with the combination of thepinned layer (310 or 330) and AP pinned layer (340 or 345), as describedabove.

Clearly, other embodiments and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. While the description of the enhanced double tunnel junctionsensor is described in relation to a magnetic disk drive read/writehead, it should understood that in other applications, the enhanceddouble tunnel junction sensor may be used alone or in combination withother devices. Therefore, the disclosed invention is to be consideredmerely illustrative and limited in scope only as specified in theappended claims.

What is claimed is:
 1. A resonant enhanced double tunnel junction sensorthat has an air bearing surface (ABS) comprising: an electricallyconductive first shield layer; an electrically conductive firstantiferromagnetic pinning layer that has a magnetic moment oriented in afirst predetermined direction; an electrically conductive firstferromagnetic pinned layer exchange coupled to the first pinning layerso that a magnetic moment of the first pinned layer is pinned in thefirst predetermined direction; a first enhancement layer capable ofenhancing spin polarized resonant tunneling; a first spacer layer; aferromagnetic free layer that has a magnetic moment in a secondpredetermined direction, the second predetermined direction beingdifferent than the first direction, the magnetic moment being free torotate relative to the second predetermined direction in response to anapplied magnetic field; a second spacer layer; a second enhancementlayer capable of enhancing spin polarized resonant tunneling; anelectrically conductive second ferromagnetic pinned layer; anelectrically conductive second antiferromagnetic pinning layer that hasmagnetic spins oriented in the first predetermined direction and byexchange coupling pins the magnetic moment of the second pinned layer inthe first predetermined direction; and an electrically conductive secondshield layer.
 2. A resonant enhanced double tunnel junction sensor asclaimed in claim 1 wherein the first and second shield layers are usedfor electrical leads.
 3. A resonant enhanced double tunnel junctionsensor as claimed in claim 1 wherein the electrically conductive firstand second antiferromagnetic pinning layers have a thickness from 50 Åto 250 Å.
 4. A resonant enhanced double tunnel junction sensor asclaimed in claim wherein the conductive antiferromagnetic pinning layersare selected from the group PtMn, MnFe, NiMn, and IrMn.
 5. A resonantenhanced double tunnel junction sensor as claimed in claim 1 wherein theelectrically conductive first and second ferromagnetic pinned layershave a thickness from 20 Å to 60 Å.
 6. A resonant enhanced double tunneljunction sensor as claimed in claim wherein the ferromagnetic pinnedlayers are selected from the group consisting of Co₉₀Fe₁₀, NiFe and Co.7. A resonant enhanced double tunnel junction sensor as claimed in claim1 wherein the first ferromagnetic pinned layer is an antiparallel (AP)pinned layer that includes: a ruthenium (Ru) film layer and first andsecond ferromagnetic pinned film layers; the ruthenium layer beinglocated between the first pinned film layer and the second pinned filmlayer; the first pinned film layer exchange coupled to the first pinninglayer so that a magnetic moment of the first pinned film layer is pinnedin the first predetermined direction; and the second pinned film layerhaving a magnetic moment in a third direction, the third direction beingantiparallel to the first direction.
 8. A resonant enhanced doubletunnel junction sensor as claimed in claim 7 wherein the first andsecond pinned film layers are made from cobalt (Co).
 9. A resonantenhanced double tunnel junction sensor as claimed in claim 8 wherein thefirst and second pinned film layers have a thickness of 25 Å and 20 Årespectively and the ruthenium layer has a thickness of 8 Å.
 10. Aresonant enhanced double tunnel junction sensor as claimed in claim 7wherein the second ferromagnetic pinned layer is an antiparallel (AP)pinned layer that includes: a ruthenium (Ru) film layer and third andforth ferromagnetic pinned film layers; the ruthenium layer beinglocated between the third pinned film layer and the forth pinned filmlayer; the forth pinned film layer exchange coupled to the secondpinning layer so that a magnetic moment of the forth pinned film layeris pinned in the first predetermined direction; and the third pinnedfilm layer having a magnetic moment in a third direction, the thirddirection being antiparallel to the first direction.
 11. A resonantenhanced double tunnel junction sensor as claimed in claim 10 whereinthe third and forth pinned film layers are made from cobalt (Co).
 12. Aresonant enhanced double tunnel junction sensor as claimed in claim 11wherein the third and forth pinned film layers have a thickness of 20 Åand 25 Å respectively and the ruthenium layer has a thickness of 8 Å.13. A resonant enhanced double tunnel junction sensor as claimed inclaim 1 wherein the first and second enhancement layers have a thicknessof 10 Å.
 14. A resonant enhanced double tunnel junction sensor asclaimed in claim 13 wherein the enhancement layers are made from Cu orAl.
 15. A resonant enhanced double tunnel junction sensor as claimed inclaim 1 wherein the first and second spacer layers have a thickness from10 Å to 30 Å.
 16. A resonant enhanced double tunnel junction sensor asclaimed in claim 15 wherein the spacer layers are made from aluminumoxide.
 17. A resonant enhanced double tunnel junction sensor as claimedin claim 1 wherein the ferromagnetic alloy free layer has a thicknessfrom 30 Å to 100 Å.
 18. A resonant enhanced double tunnel junctionsensor as claimed in claim 17 wherein the ferromagnetic alloy free layeris made from NiFe.
 19. A resonant enhanced double tunnel junction sensoras claimed in claim 17 wherein the ferromagnetic alloy free layer ismade from a combination of 25% Co₉₀Fe₁₀ and 75% NiFe.
 20. A resonantenhanced double tunnel junction sensor as claimed in claim 1 wherein thefirst and second shields are made from Permalloy (Ni₈₀Fe₂₀).
 21. Aresonant enhanced double tunnel junction sensor as claimed in claim 1wherein the first predetermined direction being normal to the ABS.
 22. Amagnetic head that has an air bearing surface (ABS) comprising: a readhead that includes: a resonant enhanced double tunnel junction sensorresponsive to applied magnetic fields; first and second electricallyconductive lead layers connected to the double tunnel junction sensorfor conducting a tunnel current through the double tunnel junctionsensor; the double tunnel junction sensor including: an electricallyconductive first shield layer; an electrically conductive firstantiferromagnetic pinning layer that has magnetic spins oriented in afirst predetermined direction; an electrically conductive firstferromagnetic pinned layer exchange coupled to the first pinning layerso that a magnetic moment of the first pinned layer is pinned in thefirst predetermined direction; a first enhancement layer capable ofenhancing spin polarized resonant tunneling; a first spacer layer; aferromagnetic free layer that has a magnetic moment in a secondpredetermined direction, the second predetermined direction beingdifferent than the first direction, the magnetic moment being free torotate relative to the second predetermined direction in response to anapplied magnetic field; a second spacer layer; a second enhancementlayer capable of enhancing spin polarized resonant tunneling; anelectrically conductive second ferromagnetic pinned layer; anelectrically conductive second antiferromagnetic pinning layer that hasmagnetic spins oriented in the first predetermined direction and byexchange coupling pins the magnetic moment of the second pinned layer inthe first predetermined direction; and an electrically conductive secondshield layer; a write head including: first and second pole piece layersand a write gap layer; the first and second pole piece layers beingseparated by the write gap layer at the ABS and connected at a back gapthat is recessed rearwardly in the head from the ABS; an insulationstack having at least first and second insulation layers; at least onecoil layer embedded in the insulation stack; and the insulation stackand the at least one coil layer being located between the first andsecond pole piece layers.
 23. A magnetic head as claimed in claim 22wherein the first and second electrically conductive lead layers are theelectrically conductive first and second shield layers.
 24. A magnetichead as claimed in claim 22 wherein the electrically conductive firstand second antiferromagnetic pinning layers have a thickness from 50 Åto 250 Å.
 25. A magnetic head as claimed in claim 24 wherein theconductive antiferromagnetic pinning layers are selected from the groupPtMn, MnFe, NiMn, and IrMn.
 26. A magnetic head as claimed in claim 22wherein the electrically conductive first and second ferromagneticpinned layers have a thickness from 20 Å to 60 Å.
 27. A magnetic head asclaimed in claim 26 wherein the ferromagnetic pinned layers are selectedfrom the group consisting of Co₉₀Fe₁₀, NiFe and Co.
 28. A magnetic headas claimed in claim 22 wherein the first ferromagnetic pinned layer isan antiparallel (AP) pinned layer that includes: a ruthenium (Ru) filmlayer and first and second ferromagnetic pinned film layers; theruthenium layer being located between the first pinned film layer andthe second pinned film layer; the first pinned film layer exchangecoupled to the first pinning layer so that a magnetic moment of thefirst pinned film layer is pinned in the first predetermined direction;and the second pinned film layer having a magnetic moment in a thirddirection, the third direction being antiparallel to the firstdirection.
 29. A magnetic head as claimed in claim 28 wherein the firstand second pinned film layers are made from cobalt (Co).
 30. A magnetichead as claimed in claim 29 wherein the first and second pinned filmlayers have a thickness of 25 Å and 20 Å respectively and the rutheniumlayer has a thickness of 8 Å.
 31. A magnetic head as claimed in claim 28wherein the second ferromagnetic pinned layer is an antiparallel (AP)pinned layer that includes: a ruthenium (Ru) film layer and third andforth ferromagnetic pinned film layers; the ruthenium layer beinglocated between the third pinned film layer and the forth pinned filmlayer; the forth pinned film layer exchange coupled to the secondpinning layer so that a magnetic moment of the forth pinned film layeris pinned in the first predetermined direction; and the third pinnedfilm layer having a magnetic moment in a third direction, the thirddirection being antiparallel to the first direction.
 32. A magnetic headas claimed in claim 31 wherein the third and forth pinned film layersare made from cobalt (Co).
 33. A magnetic head as claimed in claim 32wherein the third and forth pinned film layers have a thickness of 20 Åand 25 Å respectively and the ruthenium layer has a thickness of 8 Å.34. A magnetic head as claimed in claim 22 wherein the first and secondenhancement layers have a thickness of 10 Å.
 35. A magnetic head asclaimed in claim 34 wherein the enhancement layers are made from Cu orAl.
 36. A magnetic head as claimed in claim 22 wherein the first andsecond spacer layers have a thickness from 10 Å to 30 Å.
 37. A magnetichead as claimed in claim 36 wherein the spacer layers are made fromaluminum oxide.
 38. A magnetic head as claimed in claim 22 wherein theferromagnetic alloy free layer has a thickness from 30 Å to 100 Å.
 39. Amagnetic head as claimed in claim 38 wherein the ferromagnetic alloyfree layer is made from NiFe.
 40. A magnetic head as claimed in claim 38wherein the ferromagnetic alloy free layer is made from a combination of25% Co₉₀Fe₁₀ and 75% NiFe.
 41. A magnetic head as claimed in claim 22wherein the first and second shields are made from Permalloy (Ni₈₀Fe₂₀).42. A magnetic head as claimed in claim 22 wherein the firstpredetermined direction being normal to the ABS.
 43. A magnetic diskdrive, comprising: the magnetic head including a combined read head andwrite head, said magnetic head having an air bearing surface (ABS); theread head including: a resonant enhanced double tunnel junction sensorresponsive to applied magnetic fields; and first and second electricallyconductive lead layers connected to the double tunnel junction sensorfor conducting a tunnel current through the double tunnel junctionsensor; the double tunnel junction sensor including: an electricallyconductive first shield layer; an electrically conductive firstantiferromagnetic pinning layer that has magnetic spins oriented in afirst predetermined direction; an electrically conductive firstferromagnetic pinned layer exchange coupled to the first pinning layerso that a magnetic moment of the first pinned layer is pinned in thefirst predetermined direction; a first enhancement layer capable ofenhancing spin polarized resonant tunneling; a first spacer layer; aferromagnetic free layer that has a magnetic moment in a secondpredetermined direction, the second predetermined direction beingdifferent than the first direction, the magnetic moment being free torotate relative to the second predetermined direction in response to anapplied magnetic field; a second spacer layer; a second enhancementlayer capable of enhancing spin polarized resonant tunneling; anelectrically conductive second ferromagnetic pinned layer; anelectrically conductive second antiferromagnetic pinning layer that hasmagnetic spins oriented in the first predetermined direction and byexchange coupling pins the magnetic moment of the second pinned layer inthe first predetermined direction; and an electrically conductive secondshield layer; the write head including: first and second pole piecelayers and a write gap layer wherein the first pole piece layer and thesecond shield layer are a common layer; the first and second pole piecelayers being separated by the write gap layer at the ABS and connectedat a back gap that is recessed rearwardly in the head from the ABS; aninsulation stack having at least first and second insulation layers; atleast one coil layer embedded in the insulation stack; and theinsulation stack and the at least one coil layer being located betweenthe first and second pole piece layers; a frame; a magnetic diskrotatably supported on the frame; a support mounted on the frame forsupporting the magnetic head with its ABS facing the magnetic disk sothat the magnetic head is in a transducing relationship with themagnetic disk; means for rotating the magnetic disk; positioning meansconnected to the support for moving the magnetic head to multiplepositions with respect to said magnetic disk; and processing meansconnected to the magnetic head, to the means for rotating the magneticdisk and to the positioning means for exchanging signals with the mergedmagnetic head, for controlling movement of the magnetic disk and forcontrolling the position of the magnetic head.
 44. A magnetic disk driveas claimed in claim 43 wherein the processing means is connected to thefirst and second leads for applying the tunnel current to the sensor.45. A magnetic disk drive as claimed in claim 44 wherein the processingmeans applies said tunnel current.
 46. A magnetic disk drive as claimedin claim 43 wherein the first and second electrically conductive leadlayers are the electrically conductive first and second shield layers.47. A magnetic disk drive as claimed in claim 43 wherein theelectrically conductive first and second antiferromagnetic pinninglayers have a thickness from 50 Å to 250 Å.
 48. A magnetic disk drive asclaimed in claim 47 wherein the conductive antiferromagnetic pinninglayers are selected from the group PtMn, MnFe, NiMn, and IrMn.
 49. Amagnetic disk drive as claimed in claim 43 wherein the electricallyconductive first and second ferromagnetic pinned layers have a thicknessfrom 20 Å to 60 Å.
 50. A magnetic disk drive as claimed in claim 49wherein the ferromagnetic pinned layers are selected from the groupconsisting of Co₉₀Fe₁₀, NiFe and Co.
 51. A magnetic disk drive asclaimed in claim 43 wherein the first ferromagnetic pinned layer is anantiparallel (AP) pinned layer that includes: a ruthenium (Ru) filmlayer and first and second ferromagnetic pinned film layers; theruthenium layer being located between the first pinned film layer andthe second pinned film layer; the first pinned film layer exchangecoupled to the first pinning layer so that a magnetic moment of thefirst pinned film layer is pinned in the first predetermined direction;and the second pinned film layer having a magnetic moment in a thirddirection, the third direction being antiparallel to the firstdirection.
 52. A magnetic disk drive as claimed in claim 51 wherein thefirst and second pinned film layers are made from cobalt (Co).
 53. Amagnetic disk drive as claimed in claim 52 wherein the first and secondpinned film layers have a thickness of 25 Å and 20 Å respectively andthe ruthenium layer has a thickness of 8 Å.
 54. A magnetic disk drive asclaimed in claim 51 wherein the second ferromagnetic pinned layer is anantiparallel (AP) pinned layer that includes: a ruthenium (Ru) filmlayer and third and forth ferromagnetic pinned film layers; theruthenium layer being located between the third pinned film layer andthe forth pinned film layer; the forth pinned film layer exchangecoupled to the second pinning layer so that a magnetic moment of theforth pinned film layer is pinned in the first predetermined direction;and the third pinned film layer having a magnetic moment in a thirddirection, the third direction being antiparallel to the firstdirection.
 55. A magnetic disk drive as claimed in claim 54 wherein thethird and forth pinned film layers are made from cobalt (Co).
 56. Amagnetic disk drive as claimed in claim 55 wherein the third and forthpinned film layers have a thickness of 20 Å and 25 Å respectively andthe ruthenium layer has a thickness of 8 Å.
 57. A magnetic disk drive asclaimed in claim 43 wherein the first and second enhancement layers havea thickness of 10 Å.
 58. A magnetic disk drive as claimed in claim 57wherein the enhancement layers are made from Cu or Al.
 59. A magneticdisk drive as claimed in claim 43 wherein the first and second spacerlayers have a thickness from 10 Å to 30 Å.
 60. A magnetic disk drive asclaimed in claim 59 wherein the spacer layers are made from aluminumoxide.
 61. A magnetic disk drive as claimed in claim 43 wherein theferromagnetic alloy free layer has a thickness from 30 Å to 100 Å.
 62. Amagnetic disk drive as claimed in claim 61 wherein the ferromagneticalloy free layer is made from NiFe.
 63. A magnetic disk drive as claimedin claim 61 wherein the ferromagnetic alloy free layer is made from acombination of 25% Co₉₀Fe₁₀ and 75% NiFe.
 64. A magnetic disk drive asclaimed in claim 43 wherein the first and second shields are made fromPermalloy (Ni₈₀Fe₂₀).
 65. A magnetic disk drive as claimed in claim 43wherein the first predetermined direction being normal to the ABS.